The use of various types of water treatment chemicals for controlling biological activity such as spores, bacteria, viruses, allergy, fungi, and any other biological phenomenon that adversely affects the quality of water is well known. Chemicals added to water for the purpose of controlling scaling and corrosion are also known. Such chemicals are often used in recreational water such as swimming pools, theme parks, in industrial or commercial process water such as cooling towers and for sewage treatment and the like, and in drinking water. In light of today's increased environmental awareness, the need to both minimize the types of chemicals that are routed for sewage treatment and preserve water as a valuable resource and, therefore, the need to maximize the use and recyclability of water used for both industrial and recreational applications, is greater than ever. Accordingly, in order to maximize the utility and recyclability of the water being used in such applications it is desired that the chemical agents used to treat the water be effective in controlling biological activity, corrosion, and scaling so that the water can be reused over and over again and any blowdown water be free of noxious or toxic materials.
The use of chlorine for disinfecting bodies of water such as, swimming pools, baths, reservoirs, cooling tower water, recreational water, or any form of water that is exposed to the open air, is well known. In the past, chlorine has usually been supplied by direct application of chlorine gas (Cl.sub.2) from tanks containing the gas under pressure. Chlorine has also been supplied by electrolytic generation via an electrolytic cell. Other chlorine containing gas species such as chlorine dioxide (ClO.sub.2) have also been used in disinfecting bodies of water. Chlorine dioxide is a dangerous and explosive gas and is usually produced as an aqueous solution at the point of usage by chemical decomposition of chlorine salt. Production of chlorine dioxide electrochemically from chlorides was also unknown in the literature prior to about 1982.
Lindstaedt U.S. Pat. No. 2,887,444 discloses a system in which a body of water, such as a swimming pool, is provided with a low concentration of dissolved common salt and a stream of water is removed from the main body and electrolyzed to produce chlorine, and the chlorine and water stream are returned to the main body of water.
Murray U.S. Pat. No. 3,223,242 discloses another type of electrolytic cell for generating chlorine for introduction into a stream of water removed from and introduced back into a swimming pool or other body of water.
Richards U.S. Pat. No. 3,282,823 discloses an electrolytic cell for production of chlorine positioned in-line for introducing chlorine into a stream of water removed from and reintroduced into a swimming pool.
Other chlorinating systems using electrolytic cells for chlorinating bodies of water are shown in Oldershaw U.S. Pat. No. 3,351,542, Colvin U.S. Pat. No. 3,378,479, Kirkham U.S. Pat. No. 3,669,857 and Yates U.S. Pat No. 4,097,356. These electrolytic cells are disclosed in a variety of configurations and most of the cells utilize ion-permeable membranes separating the anode and cathode-containing compartments.
Ion-permeable membrane technology used in electrolytic cells is well developed. Ion-permeable membranes used in electrolytic cells have ranged from asbestos diaphragms to carboxylate resin polymers to perfluorosulfonic acid polymer membranes. The perfluorosulfonic acid membranes were developed by Dupont for use in electrolytic cells.
Dotson U.S. Pat. No. 3,793,163 discloses the use of Dupont perfluorosulfonic acid membranes in electrolytic cells and makes reference to U.S. Pat. Nos. 2,636,851; 3,017,338, 3,560,568; 3,4696,077; 2,967,807; 3,282,875 and British Pat. No. 1,184,321 as discussing such membranes and various uses thereof.
Walmsley U.S. Pat. No. 3,909,378 discloses another type of fluorinated ion exchange polymer used in membranes for electrolytic cells for electrolysis of salt solutions.
Further discussion of membrane technology used in electrolytic cells may be found in Butler U.S. Pat. No. 3,017,338, Danna U.S. Pat. No. 3,775,272, Kircher U.S. Pat. No. 3,960,697, Carlin U.S. Pat No. 4,010,085 and Westerlund U.S. Pat. No. 4,069,128.
Use of perfluorosulfonic acid membrane is also discussed in the technical literature, e.g. Dupont Magazine, May-June 1973, pages 22-25 and a paper entitled: "Perfluorinated on Exchange Membrane" by Grot, Munn, and Walmsley, presented to the 141st National Meeting of the Electrochemical Society, Houston, Tex., May 7-11, 1972.
The structure of electrodes used in electrolytic cells is set forth the previously listed patents. Additionally, the following patents show particular configurations of anodes or cathodes used in such cells.
Giacopelli U.S. Pat. No. 3,375,184 discloses an electrolytic cell with controllable multiple electrodes which are flat plates in electroplating cells.
Lohreberg U.S. Pat. No. 3,951,767 discloses the use of flat plate electrolytic anodes having grooves along the bottoms thereof for conducting gas bubbles generated in the electrolytic process.
Andreoli U.S. Pat. No. 565,953 discloses electroplating apparatus having a plurality of metal screens which are not connected in the electric circuit and function to plate out the metal being separated by the electrolysis.
In "The ClO.sub.2 content of chlorine obtained by electrolysis of NaCl," Electrochemical Technology 5, 56-58 (1967) Western and Hoogland report that ClO.sub.2 is not produced in the electrolysis of NaCl in the absence of chlorates.
Sweeney U.S. Pat. No. 4,256,552 discloses an electrolytic generator for chlorination of swimming pools, water systems, etc., in which a bipolar electrode is positioned in an anode compartment between an anode and an cation-exchange membrane in the wall separating the compartments.
Sweeney U.S. Pat. No. 4,334,968 discloses improvements on the cell or generator of U.S. Pat. No. 4,256,552 and discloses the production of chlorine dioxide in the cell.
Sweeney U.S. Pat. No. 4,248,681 discloses a method of producing chlorine/chlorine dioxide mixtures in the cells of U.S. Pat. Nos. 4,256,552 and 4,334,968 and gives some optimum operating conditions.
Sweeney U.S. Pat. No. 4,308,117 discloses a cell having three compartments, with an anode and cathode in the outer compartments and a bipolar electrode in the central compartment. A cation-exchange membrane is positioned in the wall between the central compartment and the cathode compartment, while an anion-exchange membrane is positioned in the wall between the central compartment and the anode compartment.
Sweeney U.S. Pat. No. 4,324,635 discloses a cell having an anode compartment, a cathode compartment, and a separating wall comprising a cation-exchange membrane therein. The cell includes a pump for circulating some of the cathode solution from the cathode compartment to the anode compartment for pH control.
Sweeney U.S. Pat. No. 4,804,449 discloses an electrolytic generator comprising an anode compartment, a cathode compartment, at least one wall separating the anode and cathode compartment comprising an ion exchange membrane therein, and at least one bipolar electrode positioned either in the anode or cathode compartment.
It has been discovered that an optimum degree of control over biological activity, scaling, and corrosion may be realized by using a gas composition comprising a mixture of chlorine gas and chlorine dioxide gas. The electrolytic devices disclosed in the above-referenced patents are concerned mainly with the generation of chlorine gas via electrolytic reaction. Many of the above-referenced patents generate the chlorine gas using a batch-type operation rather than a continuous-type operation. The use of a batch-type system is known to cause variations in the composition of the gas species produced as the concentration of the electrolyte changes during use, ultimately limiting the effectiveness of such systems. Additionally, many of the electrolytic cells known in the art operate in an electrically inefficient manner due to their construction, requiring a large input of voltage to both overcome the internal resistance of the electrolytic cell and achieve the desired electrochemical reaction.
It is, therefore, desirable that an electrolytic cell be constructed in a manner that will allow the generation of a mixed oxidant gas comprising chlorine and chlorine dioxide in a predetermined ratio to effect maximum control of biological activity, scaling, and corrosion in a body of water. It is desirable that the electrolytic cell be constructed in a manner facilitating the generation of the chlorine gas and chlorine dioxide gas in a preferred proportion without variations in such proportion during the operation of the electrolytic cell.
It is desirable that the electrolytic cell be constructed in a manner which promotes high electrical efficiency, thereby utilizing energy more efficiently in achieving the desired electrolytic reactions and producing the desired gases. It is desirable that the electrolytic cell be constructed in a manner that facilitates its operation and service in the field. It is also desirable that the electrolytic cell be constructed in a manner that is practical from both a manufacturing and an economic viewpoint.